Typically, a composite article is constructed of a plurality of plies. The plies are layered in register to conform to the plan shape of a finished article. The plies of some articles are cut from a resinous matrix preimpregnated composite sheet (called a prepreg). The cut plies are layered and cured in a molding die (usually at high temperature and pressure) to form the finished article. The prepreg sheets are supplied from a continuous roll. Each roll has a layer of paper positioned between each wrap thereof to prevent the wraps from sticking to one another.
The prepreg plies may be cut into desired shapes by a computer controlled cutter. The computer controlled cutter cuts each ply from a sheet according to programmed instructions which detail each shape. Computerized cutting has several drawbacks; the process is generally slow as each ply is cut individually, and it is difficult to verify whether complete and proper cuts have been made because each cut ply remains within the prepreg waste (or "skeleton") after cutting. It is particularly important to have complete cuts passing through the prepreg to avoid manual intervention to cut the plies from the skeleton, and to allow automated machinery, which is used to stack the plies, to lift the cut plies from the skeleton without interference therefrom.
Steel rule dies have been used to simultaneously cut a plurality of plies from a plurality of stacked prepreg sheets. Steel rule dies are generally comprised of a plurality of knife edges that are set into a backing board. The knife edges form the perimeter of a shape of a ply to be cut. The cutting process includes; unrolling a roll of prepreg to cut sheets therefrom, layering (or stacking) several sheets on top of one another, utilizing the steel rule die to cut the desired plies, separating each ply from the stacks thereof, marking each ply so that each ply may be properly placed (laid up) to form the article, and removing the paper from each ply prior to laying up each ply. Such a process is time consuming, labor intensive and prone to error.
Accordingly, there remains a continuing need in the art for an improved method and apparatus for cutting plies of material.